Assuming the drive is an Ultra2 drive or later (later being Ultra160 and Ultra320) and is a 68-pin type, you would need a SCSI card such as the LSI Logic Ultra160 (Newgg has them around $30) and an LVD cable and terminator.
An older 18GB drive may not be worth the expense, however... 10000rpm SCSI drives are in their seventh generation now, and performance gets higher with each successive generation. I have a 9GB first-generation 10k SCSI drive and in seek-intensive tasks, it's a little faster than a WD800JB ATA drive, but if you look at its flat-out sprint, it's down around 24MB/sec max. Nothing to write home about.
If you know what model of drive it is, that could help figure out where it fits in the spectrum
